Electrophotographic apparatus



Sept' 12, 1944. c. F. CARLSON 2,357,809

ELEGTRO-PHOTOGRAPHIC APPARATUS vFiled NOV. 16, 1940 k5 Sheets-Sheet lINVENTOR @ME-FM Sept 12, 1944. c. F. cARLlsoN 2,357,809

` ELECTRO PHOTO GRAPHI C APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 2INVENTOR sim* Sept. 12, 1944.

c. F. CARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 5'FY'N 9&2

\l&\ m j Q 21@ u QQ 5s N Y x Q N N w kg INVENTOR .Sept 12, 1944. FCARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 4INVENTOR wim-W Sept. l2, 1944. c. F. CARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 5SHEET INVENTOR @mi CPO/M Patented Sept. 12, 1944 UNITED STATES PATENTOFFICE 2,357,809 ELECTROPHOTOGRAPHIC APPARATUS Chester F. Carlson,Jackson Heights, N. Y.

Application November 16, 1940, Serial No. 365,888

20 Claims.

This invention relates to photographic devices and particularly todevices for use in electrophotography.

An object of the invention is to improve devices for use inelectrophotography, particularly electrophoto reproducing and copyingequipment.

Another object is to produce an electrophoto copying machine which issubstantially automatic in operation.

Further objects are to improve various parts of electrophoto reproducingapparatus.

Other objects of the invention will be apparent from the followingdescription and accompanying drawings taken in connection with theappended claims.

The invention comprises the features of construction, combination ofelements, arrangement of parts, and methods of manufacture and operationreferred to above or which will be brought out and exemplified in thedisclosure hereinafter set forth, including the illustrations in thedrawings.

In the drawings:

Figure 1 is a top view of a copying machine embodying features of thepresent invention, part of the top casing being cut away;

Figure 2 is a vertical section on the line 2-2 of Figure 1;

Figure 3 is a vertical section on the line 3-3 of Figure 2;

Figure 4 is a diagram of the electric circuit for the machine of Figures1 to 3;

Figure 5 is a vertical section of a modified copying machine accordingto the invention;

Figure 6 illustrates a circuit therefor;

Figure '7 shows a modified charging device;

Figure 8 illustrates a belt discharge attachment; I

Figure 9 represents a modified transfer mechanism; and

Figures 10 and 11 show special forms of electrophoto plates.

In my co-pending application Serial Number 265,925, led April 4, 1939,now Patent No. 2,297,691 of October 6, 1942, is described a methodl ofphotography which may be termed electrophotography and which in itspreferred embodiment comprises charging the surface of a layer ofphoto-conductive insulating material supported on a conductive backingwith an electric charge, then exposing the layerto a light image todischarge the charge in the illuminated areas and leave an electrostaticlatent image on the layer corresponding to the light image. The latentimage is subsequently developed by applying finely dividedelectrostatically attractable material, such as powder, to the surfacewhere it is retained in the charged areas by the charge therebyproducing a visible deposited image. The deposited image may then betransferred to a paper sheet.

The present invention relates to the machines and devices for carryingout such a process and contemplates a substantially automatic machinefor performing the necessary functions in sequence. The -invention alsorelates to improved parts and devices for use in the process.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the construction of parts without departing from thespirit of the invention. In the following description and in the claims,parts will be identified by specific names for convenience, but they areintended to be as generic in their application to similar parts as theart will permit.

Referring to the drawings, Figures 1 to 3 illustrate an automaticcopying machine for making single copies of original records such astracings of drawings, films, typewritten letters and generally anythingdrawn, written or printed on transparent or translucent sheets.

The machine comprises a sheet metal frame including a bottom plate 20and a pair of spaced parallel side Walls 2| and 22 from which theoperating parts are supported.

The photosensitive plate comprising a sheet of metal foil or metallizedpaper 23 having a layer 24 of photo-conductive insulating material (forexample, sulfur or anthracene) adhering to its outside surface isclamped over the outer surface of a metal drum 25 secured to an axialdrive shaft 2B which is pivoted in bearings 2'! mounted in the two sidewalls 2| and 22. Foil 23 extends about one-third of the distance aroundthe drum and is clamped at its ends under metal strips 28 inlongitudinal slots in the drum surface.

Drive shaft 26 carries a large gear wheel 29 which is driven by a worm30 on the shaft of controlled speed electric motor 3l mounted on theoutside of side wall 2|. Means are provided for starting and stoppingthe motor so as to rotate drum 25 through one revolution at a time fromthe starting position shown, as will be described later. The drumrotates in a clockwise direction as seen in Figure 2.

A roller 32 covered with a brushl or plush cover 33 is mounted on adrive shaft 34 pivoted in bearings 35. the roller being mounted in sucha posi.. tion that the plush surface is in contact with the surface ofdrum 25 in a path extending longitudinal of the drum and is at theleading edge of foil 23 when the drum is in starting position. Thesurface of drum 25 is of aluminum or chromium or other metal which doesnot readily produce any loose oxide, sulphide or other dirt, since it isof considerable importance that the operating surfaces be kept clean andparticularly free of any loose conductive material.

Plush-covered roller 32 is rapidly driven by a motor 36 mounted on theoutside of side wall 2l and coupled to the end of shaft 34. Motor 3Soperates whenever motor 3l is operating. Roller 32 is preferably rotatedin a clockwise directionas shown in Figure 2. A metal rod 31 issupported from the side walls so as to loosely touch the surface ofplush 33 to drain oi any electric charge from the plush.

Immediately to the right of roller 32 as seen in Figure 2 is a paper`feed slot formed by a pair of spaced sheet metal plates 38 and 39 whichextend across between side walls 2l and 22 and are nearly vertical. Thelower end of plate 33 terminates just short of the surface of drum 25and plate 38 is somewhat shorter. The plates are curved away from eachother at the top of the machine to form a slot into which a sheet mayreadily be inserted.

A rod 40 is pivoted along the lower edge of plate 39 and has severalspring fingers 4l extending out from it to normally press against thelower edge of plate 38, held by bias spring 42 secured to side wall 2l.A cam 43 mounted on shaft 26 co-operates with a cam-following arm 44 onthe end of rod 4D to move spring fingers 4| away from plate 38 andrelease the sheet original to be copied from the slot at the properstage of rotation of drum 25.

A frame carrying a pair of spaced parallel flanged rollers 46 and 41upon which is mounted an endless transparent belt 48 is spring-pressedagainst drum 25 immediately below the feed slot. The frame comprises apair of end plates 45 clamped in spaced parallel relation by rods 49upon which rollers 46 and 41 are pivoted. The frame is spring-pressedtoward drum 25 by coil springs 50 mounted in side walls 2l and 22 andbearing against bolts secured to the frame plates 45. Beltl 48 is aswide as drum 25 and of such length as to be drawn firmly against thedrum surface when rollers 46 and 41 are in contact with the drum. Henceas the drum rotates the transparent belt 48 rolls against the drumsurface. The belt may be of cellulose acetate sheet reinforced at theedges with Scotch tape or cemented cloth strips, or it may be a flexiblevinyl resin or other transparent flexible sheet material.

Rollers 46 and 41 are spaced apart to leave an opening equal to aboutone-fourth the circumference of drum 25 or less and a source ofillumination is mounted so as to illuminate this opening. This comprisesone or more incandescent lamps, such as lamp 52 and a light confiningand directing box 54. If desired, a light diffusing screen may beinterposed, or belt 48 made translucent to diffuse the light.

A trough 55 containing an electrostaticallyattractable powder 56 and arotatable brush agitator 51 is mounted underneath drum 25 with the opentop of the trough substantially closed by the surface of drum 25 withjust sufflcient spacing between the drum and trough edges to provideoperating clearance. Brush 51 comprises a central shaft 58 havingbristles extending radially from it in all directions. Shaft 58 ispivoted in bearings in the ends of trough and rotated at relatively slowspeed by electric gear motor 59 whenever the machine is operated. Ametal rod 60 extends longitudinally of trough 55 near the top surface ofbrush 51 to flip the ends of the bristles as they pass thus throwingdust particles 56 into the air of the trough chamber.

Powder 56 may be manually introduced into trough 55 in small chargesthrough aperture 6l as it becomes depleted. Any of a variety of powderscan be used. The powder must be such as to adhere to an electrostaticcharge on layer 24 and should be in a finely divided state. Suitablepowders are dyed thermoadhesive resins such as rosin, gum copal, gumsandarac, Vinsol, ethyl cellulose, Egyptian asphalt and the like.

A very satisfactory thermoadhesive powder can be produced by dissolvingequal parts of ethyl cellulose and Vinsol resin in acetone together witha small amount of spirit soluble aniline dye such as nigrosine oraniline blue and spray-drying the solution to produce an extremely nepowder having substantially spherical particles. Dyed lycopodium powderis suitable where thermoadhesive properties are not required of thepowder, as is also starch, cellulose flour, powdered metal and carbonpowder.

Whether fusible, thermoadhesive or non-fusible powders or others areused the particle size is preferably near the limit of definition of theeye under ordinary reading conditions. Excessive powder size contributesto graininess in appearance of the image. On the other hand extremelyfine powder may be undesirable in many instances due to its tendency toball up or cling together in clusters and also to the possibility ofextremely ne powder particles clinging to the photoconductive layer andinterfering with the proper functioning of the layer. It is desirable,therefore, to use a powder in which substantially all the particles arewithin the size range from 0.1 to 1 mil. If spherical powders are usedthis refers to their diameter, otherwise to the largest dimension. Formost purposes it is preferred to use an equidimensional powder particle,the sphere being the preferred form. A still more limited preferredrange of sizes may be given as from 0.3 to 0.8 mil.

A roller mechanism is provided at the left of the drum (as seen inFigure 2) for transferring the powder image from the photo-conductivesurface to a sheet of paper or like material. This comprises a pressureroll 62 of yielding material such as rubber or felt and a wetting roller'63 pressing against the under surface of roll '62 and running in atrough of water or other liquid 64. Pressure roll 62 is pivoted on ashaft 65 supported in end arms 66 which are spring pressed by springs 61toward main drum 25. A pair of cams 68 are mounted on shaft 26 at theends of the drum 25 and a pair of cam-following disc rollers 69 arepivoted on shaft 65 at the ends of pressure roll 62 and roll upon thecams 68. These cams are so shaped as to hold roll 62 a small fraction ofan inch away from the surface of drum 25 during the greater part of therotation of drum 25 but to allow springs 61 to press roll 62 against thephotoconductive surface 24 of plate 23 when it comes opposite the roll.

A paper feed plate 10 is tiltably mounted on pivots 'Il and extendsunder roll 52 to a position adjacent wetting roll 63. A small guideroller 12 asczsoo 3 is mounted on plate 18 to roll against pressure rolll2.

An electric oven comprising a pair of spaced parallel plate-like heatingelements 13 and 14 is mounted above feed plate 1I and generally parallelthereto and extends to a position adjacent the upper edge of pressureroll 62. Suitable paper guides 15 are mounted around roll 62 to guide asheet oi' paper around the roll from feed-plate 1I to the slot betweenelements 13 and 14 comprising the oven. The oven serves to melt theresin powder image onto the paper as will later appear.

A rotary cleaning brush 16 is mounted'above the transfer apparatus justdescribed to brush oir any retained dust from the surface of the drum orlayer 24, the brush being surrounded by a collecting chamber 11to retainthe removed dust. Brush 16 is driven by a belt or chain drive 18 fromthe shaft 34.

Figure 4 is a diagram of the preferred electric circuit for the machineabove described. Electric current from an A. C. source is used tooperate motors 3|, 36 and 59 and to energize lamp 52 and heatingelements 19 and 80 for heating plates 13 and 14.

A pair of cams 8| and 82 are mounted on the end of shaft 26 of the maindrum and control a pair of snap-acting power switches. for example,"Microswitches 83 and 84 respectively having normally-closed contactswhich are opened when their control levers are engaged by the cams.Microswitch 83 is connected in series with lamp 52 and the A. C. powerline. The cam 8| is arranged to turn olf lamp 52 when the machine is inrest position and to light the lamp during the part of the cycle whenelectrophoto layer 24 passes in front of the lamp.

A manually-controlled main switch 85 is connected in one branch of theA. C. line between the A. C. source and the motors and heating elementswith their associated controls. Heating element 88 is a quick heater forthe hot plates 13 and 14 and is connected across the line through I asnap-acting Microswitch 86 controlled by thermostat 81 mounted withinthe oven. When the oven heats up, the thermostat operates to disconnectelement from the line. Heat maintaining element 19 is a slowheaterdesigned to maintain the desired oven temperature once it has beenheated up. Element 19 is connected directly across the line.

Cam-controlled Microswitch 84 is connected between the power lineandmotors 3|, 36 and 59. A

second energizing circuit for the motors is provided, however, throughthe back (normallyopen) contacts of thermostat switch 86 and apush-button'switch 88 in series. Cam 82 is arranged to open switch 84 atthe rest position of the machine but allows switch 84 to be closedthrough the rest of the cycle. A snap switch 89 is arranged to by-passthe back contacts of thermostat switch 86 when desired.

Motors 3|, 36 and 59 have rheostats 93. 94 and respectively connected inseries with them for adjusting their speeds.

Operation To initiate operation of the machine the operator turns on thecurrent by closing snap switch 85. 'This immediately starts heatingelements 19 and 88 to heat plates 13, 14 of the oven to the desiredtemperature. As soon as this temperature is reached thermostat 81operates switch 85 to open the circuit of fast heat-up element 80 andclose the back contacts of the switch. I'his places the machine undercontrol of push-button switch 8l.

The operator in the mean time places an original sheet 88 to be copied,such as a typewritten letter, a drawing or tracing, a film or any othertranslucent design in the slot between plates 38, 39 with its lower edgeresting on ngers 4| and the written, drawn or printed side facing towarddrum 25. 'I'he operator also places a blank sheet of paper 3| on feedplate 18 with its leading edge held between rolls 62 and 12.

The operator now presses push button 88 moentarily, thereby completingenergizing circuits for motors 3|, 3-6 and 59, all of which start torotate. Motor 3| rotates drum 25 slowly in a clockwise direction (asseen in Figure 2) thereby advancing the photoconductive layer 24 underplush roller 32. Roller 32 is rapidly rotated by motor 36 and thefrictional rubbing of the plush 33 thereby creates an electrostaticcharge of substantial voltage uniformly over the surface of A roundbrush may be used in place of the plush roller, if desired.

As soon as drum 25 has rotated a few degrees cam 82 is moved out ofengagement with switch 84 allowing it to close and thereby establishinga shunt circuit around push-button 88 so that 88 may be released withoutstopping the machine. At about the same time cam 8| allows switch 83 toclose an energizing circuit for lamp 52.

Layer 24 continues to rotate and when its leading edge comes adjacentthe lower edge of the sheet 90 the cam 43 engages arm 44 to release fspring lingers 4| and thereby allow sheet 90 to slip down and enterbetween drum 25 and transparent belt 48 where it passes around roller46. As the rotation thus continues the charged photoconductive layer 24is moved past the area illuminated by lamp 52 with original sheet 90carried along tightly held against its surface by the belt 48, the imageside of sheet 90 being in direct contact with layer 24. The layer 24 isthus exposed to illumination from lamp 52 as modied by the image onsheet 90 as they pass together around that part of the drum betweenrollers 46 and 41. The illuminated areas of layer 24 are therebyrendered suillciently conductive while illuminated to allow theelectrostatic charge thereon to drain ofi' to the metal backing 23through the layer. However, where layer 24 is protected fromillumination by the dark lines or letters on sheet 90 the electrostaticcharge remains. An electrostatic latent image corresponding to a mirrorreverse of the original image is thus produced on layer 24.

As sheet 98 passes out from under belt 48 it separates from the drum andis deposited in the space 92. The layer 24 passes over the top of trough55 which, at this time, is filled With an atmosphere of floating powderparticles due to the agitation created by brush 51 driven by geareddownmotor 59. A substantial number of the dust particles are attracted bythe charge image and deposit themselves on layer 24 in a visible image.It is probable that the attracted powder particles carry an electriccharge of opposite sign to that of the electrostatic latent'image. Sincethe image produced as herein described is normally negative in chargethe deposited powder particles are prob ably positively charged. Thereare probably also negatively charged particles in the chamber which donot deposit on the image.

The layer 24 carrying its electrostatically attracted powder image iscarried around to the transfer position where the dust image istransferred to blank sheet 9|. As the leading edge of layer 24approaches roller 62 the cams 60 mounted at the ends of drum 25, whichhave so far held roller 62 out of contact with the drum, allow roller 62to come into pressure contact with the drum and be driven thereby. Asroller 62 starts to rotate it moves the leading edge of blank sheet 9|around against wetting roller 63 and up into contact with drum 25. Thesurface of sheet 9| is thereby wetted and as it rolls between roll 62and layer 24 the wet surface is pressed against and picks up the powderimage from layer 24.

Sheet 9|, due to the expansion of its wet surface and due to guides l5curls away from layer 24 as soon as it emerges from between roller 62and the drum. The sheet, carrying the adhering dust image, passesbetween hot plates 73 and 14. Since these are, at this time, heated tothe melting point, or at last the thermoadhesive point, of powder 56 thepaper is rapidly dried out and the powder image melted onto the sheet.The operator can then remove the copy from the machine by grasping thefree edge of sheet i where it projects from the upper edge of the slotbetween plates 13 and 14.

As layer 24 continues its rotation any slight moisture lm adhering to itafter the transfer rapidly evaporates and any remaining dust is cleanedfrom its surface by rotating cleaning brush 16. When one revolution ofdrum 25 has been completed cam 82 opens switch 64 to stop the rotationof all the parts. Cam 8| has opened the circuit for lamp 52 as soon asit completed its function.

If a thermoadhesive powder, such as a resin, is used a sheet of ordinarypaper 9| can be used for receiving the copy, such as a sheet of bondpaper, Manilla paper, newsprint paper, calendered paper, or almost anyother type. The image can also be transferred to a sheet alreadycarrying writing or printing, such as a letterhead or other insignia,rulings or the like. If a non-thermoadhesive powder is used it isnecessary to use a sheet 9| having a thermoadhesive coating alreadyapplied thereto such as ethyl cellulose, hard wax or a resin. In eithercase the finished copy will be a full size positive copy of theoriginal.

Figure illustrates, in section, the essential parts of a modifiedphotographic copying machine embodying a. camera having a lens forfocussing the image to be copied onto the photoconductive layer. Such amachine is capable not only of copying the translucent matter previouslymentioned but also visual intelligence on opaque sheets or on sheetshaving printing on both faces so as to interfere with copying by thecontact method.

Figure 6 is a diagram of a circuit for the machine of Figure 5.Referring to Figures 5 and 6, the layer of photoconductive insulatingmaterial |00 is deposited on an endless conductive belt |0| of flexiblematerial such as steel or other metal, or paper or other organicmaterial having a metal or other conductive surface applied thereto bymetal spraying, cathode sputtering, electroplating or chemical reductionmethods prior to deposition of the photoconductive layer. Layer |00 maycover the entire outside surface of the belt or may cover only a limitedarea as shown. Belt |0| runs on two spaced drums |02 and |03 and hassprocket holes along its edges which mesh with sprockets |04 on drum|02.

A cleaning brush |05 and a charging brush or plush roller |06 aremounted toengage the surface of belt |0| as it passes over the top ofdrum |02. Cleaning brush |05 is covered by a housing |01 provided with aduct |08 connected with a suction fan to remove extraneous dust. Thesuction duct can be dispensed with, if desired, and a removable settlingchamber provided for dust removed from the layer by brush |05.

Drum |02 and brushes |05 and |06 are driven by suitable motors '|00 andH0 respectively in a clockwise manner similar to that described forFigures 1 to 4.

A pair of dusting chambers or troughs and i I2 are mounted underneathdrum |03 with their open tops close to the surface of belt |0| and areprovided with powder agitating rotary brushes H3 and H4 of the typepreviously described. Brush ||3 is connected to the shaft of a geareddown electric motor i5 and brush I |4 to a similar motor ||6. Manuallycontrolled switches lll and ||8 are adapted to connect either or bothmotors to the energizing circuit to thereby render either or bothdusting chambers operative. Similar dusting powders ||9 may be in eachchamber or two powders may be used of differing color or othercharacteristics. Switches ||l and H8 thereby enable selection fordeposition of powders of different colors or other characteristics atthe will of the operator.

Drum |02 carries on its ends a pair of drive gears |20 which drivedriven gears |2| each carrying a cam |22. Cam following arms |23 areeach pivotally mounted on the supporting framework with one end carryinga cam following roller in the path of its associated cam |22. The otherends of the two arms support the ends of a shaft carrying pressure roll|24. Bias springs |25 on each arm normally hold the arms so that theircam followers are in the path of cams |22 and roll |24 is a fraction ofan inch away from the surface of belt |0| where the belt is held by itstension against drum |03. A paper feed plate |26, wetting roll |27 andelectric oven |28 are associated with pressure roll |24 for co-operationin a manner similar to that previously described.

The gear ratio between gears |20 and |2| is the same as the ratiobetween the circumference of drum |02 and the length of belt 80| (suchas 1:2) so that cam |22 is carried through one complete revolutionduring one completercycle of rotation of belt |0|.

Shaft |39, to which one (or both) gears |2| is secured carries a pair ofswitch actuating cams |40 and |4| for controlling switches for the drivemotors.

A camera is provided to the right of the mechanism (as shown) comprisinga plate |30 supporting the sheet |3| carrying the printing, writing,drawing, or pictorial matter to be copied. Lamps |32 and |33 forilluminating the face of the sheet are suitably disposed in front of itnear opposite edges and reflectors |35 aid in confining and directingthe light.

If desired plate |30 may be translucent and another lamp |34 may bedisposed at an appropriate distance behind plate |30 and usedsupplementary to lamps |32 and|33 where translucent sheet material is tobe copied. This results in illumination from the front and back at thesame time thus enabling more rapid exposures.

A camera lens |36 is mounted in front of sheet |3| so as to be betweensheet |3| and the straight part of belt |0|. Suitable telescopinghousings |31 permits variation of the distance .between lens |36 andsheet |3|, and a bellows |38 permits adjustment of the spacing betweenthe lens and thebelt |0| and also serves to keep out stray light. Byadjusting the positions of lens |38 and sheet I3| .an enlargement orreduction of image size is possi-ble. Instead of a sheet to be copied itis obvious that the sheet |3| and backing plate |30 may be removed topermit the photographing of 3-dimensional objects, scenes, persons andall sorts of matter capable of photographic recordings.

Lamps |32 and |33 (and |34 when used) are under the joint control ofcams |40 and |4| and a timing cam |42 driven by an electric clock motor|43. The circuit, insofar as it differs from that of Figure 4 will beapparent from reference to Figure 6 and from the following descriptionof the operation of the mechanism of Figures 5 and 6.

Assuming that it is desired to copy sheet |3|, it is placed in theposition shown, and main power switch |44 is turned on. This heats upoven |28 until thermostat |45 operates switch |46 to render manualstarting switch |41 operative. The operator places a blank sheet ofpaper on feed plate |26 and presses switch |41 to start the machine.Layer is, at this instant, at the top of its cycle under cleaning brushand as the machine starts to operate layer |00 is carried under chargingbrush |06 where it is given a surface electric charge. Cam |40 meanwhilecloses switch |48 thus removing control from switch |41.

When layer |00 is charged and carried around in front of lens |36 cam|4| opens the back contacts of switch |49 to stop the drive motor, andsimultaneously closes the front contacts to start clock motor |43driving timing cam |42. Cam |42 has low, intermediate and high camsurfaces |50, |5| and |52, which control a cam-following switch |54having an intermediate or neutral position, and front and back contactpositions` Cam |42 is connected to the shaft of motor |43 `by a one-wayratchet or clutch |53 to permit manual advance of cam |42 independent ofmotor |43. This enables the cam to be set in the position shown at thebeginning of each copying cycle. If this has, been done timing motor |43will quickly move cam |42 to a position where switch |54 is engaged bycam surface |52, allowing suiflcient time, however, before this occurs,for the drive motors and mechanism to come to a full stop so that noblurring of the image can take place.

When switch |54 is engaged by raised cam surface |52 lights lamps |32,|33 from the A. C. source through the closed contacts of switches |48,|49 and |54. The length of cam surface |52 and the speed of clock motor|43 determine the time of exposure during which the image from sheet I3| is focussed on layer |00. During this period the light from the lightareas of the image renders layer |00 conductive to dissipate the chargeheld thereon while allowing the charge in the dark areas to remain,thereby producing an electrostatic latent image on layer |00.

When clock motor |43 has moved cam |42 until lowest cam surface |50comes opposite switch |54 the cam following arm of the switch drops soas to open the energizing circuit for lamps |32, |33 and close anenergizing circuit for the drive motors through contacts of switches|48, |48 and |54. The mechanism is thereby started to move layer |00past dusting chambers and I|2 where the electrostatic image is developedand rendered visible and past transfer roll |24 which presses the moistsheet of blank paper against the layer to pick up the dust image. Cam|22 operates arms |23 at the correct instant to press roller |24 againstthe belt |0| to draw the paper sheet around against the layer at theproper time. The image, if of fusible powder, is melted onto the sheetin oven |28 as previously described. Rotation continues until the cycleis ended by the opening of switch |48 by cam |40.

Cam plate |42 is removable and can be replaced by other cams to givedifferent exposure periods.

Figure 7 shows a modified form of charging brush for the photoconductivelayer. This comprises a belt |60 running on a drive roller |6| and anidler roll |62 and having an outer plush surface |63 rubbing against thesurface of photoconductive layer |64. Surface |63 may be plush, fur,wool, woven or knit cotton, wool, silk or rayon fabric, felt, hair,velvet or other suitable charging material. A metal rod |65 may bemounted so as to just touch the surface |63 to drain olf accumulatedcharges.

Figure 8 shows an improvement applicable to the machine of Figures 1 to4 and comprises a felt wick |10 dipping in a container |1I of Water andlightly pressing against transparent belt 48 which serves to hold thesheet original against the drum. Wick |10 extends for the full beltwidth and performs the function of discharging any static charge whichmay be present on the belt and which might, in some cases, interferewith the proper discharge of the photoconductive layer. The amount ofmoisture picked up by the belt from wick |10 is so slight that the beltdries almost instantly.

Figure 9 illustrates a modied powder image transfer mechanism andcomprises a pressure roll preferably felt covered, a heater plate |8|,and oven |82. Plate |8| may comprise chromium-plated copper havingembedded insulated heating wires |83. The blank paper sheet |84 is fedbetween plate |8| and roller |80 and is advanced by roller |80 inco-operatlon with idler roll |85 mounted in an aperture in plate |8I. Assheet |84 is advanced to a position to engage the surface ofphotoconductive layer |86 carrying the electrostatically deposited resindust image its surface is heated by plate |8| to a temperature Withinthe thermosoftening range of the dust image. When paper sheet |84 isrolled against layer |86, therefore, it is hot enough to melt ontoitself the resin dust particles thereby transferring the image to thepaper. Due to the rapidity with which the operation is performed,however, layer |86 and its supporting metal base remain relatively coldand hence the powder does not stick to the layer |86 when it is tnusheated. The heat-softened or semi-melted resin does not adhere to thecold surface although it sticks readily to the hot paper. It may be thatthe adhesion will be sufficient so that iurtner nxing is not required.In such event oven |82 can be eliminated from the device or need not vbeused. It is also possible, in this as well as the other transfermechanisms to leave off the top half of the oven so that the melting ofthe resin onto the sheet may be more readily observed. Or a glass covermay be substituted for the top half of the oven.

It may be that for some copying work it will be desired to use astandard form which will appear on all copies in addition to certainmatter which will be different on different copies. Such a form maycomprise a letterhead, for example, or a trade-mark or possibly specialrulings to block off different columns or parts of the photographicallycopied matter. For this purpose a specially prepared photoconductiveplate |90 may be used comprising a metal foil base |9| having a layer|92 of photoconductive insulating material such as anthracene depositedthereon as shown in Figure 10. The standard form to be reproduced isapplied to the surface of layer |92 as an adhering layer of insulatingmaterial |93 such as resin, shellac or other charge-holding materialconforming to the design or form in mirror-reverse. Layer |93 may beapplied by printing, stamping, stencilling, drawing or by thephotographic process herein described. In the photographic process, theplate |9| carrying layer |92 is charged in the usual way, exposed to theimage of the form to be applied and dusted with resin powder. However,instead of transferring the powder image, it is left on the layer andthe layer is heated to melt the resin into the surface of layer |92,thereby producing the completed plate.

In whatever way the plate is made it functions in the following y mannerwhen used. The charging brush applies an electrostatic charge not onlyto layer |92 but also to layer |93 constituting the form. Upon exposureto alight image an electrostatic latent image is produced on the exposedareas of layer |92 as before but in addition the electric charge remainson the letters and other designs comprising layer |93 since these areasare not photoconductive. Thus when the layer is dusted the form willattract the dust as well as the photographic electrostatic latent imagepresent on the other areas. The sheet to which the dust image istransferred will therefore receive the form as well as the photographicpart of the image.

The processes and apparatus of the present invention are also adaptableto the production of master plates from which a large number of copiesmay be rapidly reproduced.

According to one method of preparing a lithographic master plate aconventional lithographie sheet of prepared aluminum, zinc or ofpaperlike composition, such as the Duplimat sheets produced for use onMultilith machines, is used in place of paper sheet 9| to receive thetransfer of the resin powder image from the photoconductive layer. Theresin is melted onto the litho sheet to complete the master suitableforoffset press operation. According to another method of producingeither a lithographie or hectograph master an electrophoto plate may beused having a metal foil backing and a photoconductive coating ofanthracene or other heat volatile photoconductive material. Arielectrostatic 1atent image is produced as previously described and thelayer is dusted with a resin powder. However, instead of transferringthe powder image the plate is removed from the machine and heated toevaporate the anthracene. The resin may melt before or after theanthracene is dispersed, depending upon its melting point, but in anyevent it is desired to nally heat the plate suiciently to melt the resinonto it. The result is a master plate such as shown in Figure 11comprising a metal foil base 20|) having a resin image 29| meltedthereon.

If the master plate is to be used for lithographic reproduction base 209should be an aluminum or zinc plate prepared for lithography and theresin should be of a type adapted to attract lithographie ink. This istrue of most resins, such as rosin. Vinsol, copal and sandarac. Ifdesired, powdered lithographie crayon can be used, or a mixture of equalparts crayon and one of the resins mentioned melted together. If theplate is to be used in the oilset process the image should not be amirror reverse, but a direct image.

If the plate is to be used for spirit duplication the resin should be atleast slightly soluble in alcohol or the other spirits to be used andshould contain a high concentration of spirit soluble dye. Copies aremade by rolling or pressing paper sheets moistened with the spiritsagainst the plate to dissolve off a little of the dye each time and thusproduce a copy.

A further multi-copy method is also possible with this plate. The resinbeing an insulator it can be electrically charged to pick up dustparticles and hence if the plate is placed in the machine of Figures 1to 3 and the machine operated copies can be produced. If this plate isused the exposure step is, of course, eliminated and lamp 52 as well asthe transparent belt and its supports can be removed from the machine,

or temporarily withdrawn from operation as they are unnecessary.

It is also contemplated that plates of the type shown in Figure l1 canbe made by other methods for use in the machine of Figures 1 to 3 in themanner described above.

Since the operation of the photographic process described herein dependsupon an electrostatic charge upon the photoconductive layer it might beassumed that high atmospheric humidity would deleteriously affect theoperation of the process. However, I have not found this to be the case,perhaps due to the non-hygroscopic nature of the photoconductivematerials used. For extreme humidity conditions it may be desirable,however, to include in the copying machines, at strategically locatedpositions, electric heating elements for slightly heating the machineparts to disperse any surface moisture. For example, heaters may belocated within the shell of the drum (or drums) against which the metalsheet carrying the photoconductive layer is held.

It is also contemplated that in some cases the dusting can be improvedby charging the electroscopic powder from an 4outside source. Forexample, the dusting chamber 55 and its associated parts may beinsulated from the rest of the machine and connected to the positiveterminal of a high voltage source such as a transformerrectifiercircuit, or an electrostatic generator. This will place a positivecharge upon a larger proportion of the dust particles so that they willmore readily deposit upon the negative charge image. y

The charge applied to the photoconductive layer by brush or plush 33 mayalso be enhanced by connecting the negative terminal of a high voltagesource to rod 3l, which rod in this case should be insulated from therest of the machine.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby but it is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial, means for charging said layer, means for projecting a iightimage onto said layer,

means for bringing a iinely-divided material ad jacent said layerl andmeans for transferring said material from said layer to animage-receptive surface, said means being adapted to cooperate with saidlayer in the sequence named.

2. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial, means for charging said layer, means for projecting a lightimage onto said layer, means for bringing a finely-divided materialadjacent said layer, and means for transferring said material from saidlayer to an image-receptive surface, and means for bringing saidelectrophoto plate into co-operative relation with said means insequence.

3. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial, a charging device for placing an electrostatic charge on saidlayer, an illuminating device for projecting a light image onto saidlayer, a dusting device for dusting said layer with a powder, a transferdevice for transferring powder from said layer to a receiving sheet, andmeans to move said plate into co-operative relation with said chargingdevice, said illuminating device, said dusting device and said transferdevice in sequence.

4. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial, means for applying an electrostatic charge image to saidlayer, means for subsequently dusting said layer with powder, and meansfor then transferring dust adhering to said layer to a flexible sheet.

5. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial, means for applying an electrostatic charge image to saidlayer, means for subsequently dusting said layer with powder, and meansfor then transferring dust adhering to said layer to a flexible sheet,and means for subsequently fixing said powder permanently to said sheet.

6. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial and means for moving said plate through a series of positionsin sequence in a path parallel to its own surface, a frictional chargingmember for electrostatically charging said layer by friction in thefirst of said positions, light image projecting means for projecting alight image onto said layer in the second of said positions, a dustingdevice for dusting said layer in the third of said positions, andtransfer means for pressing a, dust receiving sheet against said layerin the fourth of said positions.

7. An electrophotographic copying machine comprising, in combination, adrum, an electrophoto plate comprising a layer of photoconductiveinsulating material secured to the outer surface thereof, means forrotating said drum, a frictional charging brush in contact with thesurface of said drum and means for rotating said brush to charge saidlayer, means for guiding an image-carrying sheet against the surface ofsaid layer and means for illuminating said layer through said sheet, adusting chamber having an opening adjacent said drum and means forproducing a dust atmosphere in said chamber for dusting said layer, andtransfer means including a roller for rolling a transfer sheet againstsaid layer to transfer transfer sheet.

I 8. An electrophotographic camera comprising a belt having a layer ofphotoconductive insulating material thereon, guiding and driving meansfor moving said belt along in a direction substantially parallel to itsown surface, a frictional charging brush in contact with the surface ofsaid belt and means for rotating said brush to charge said layer, alens, said guiding and driving means guiding said belt in front of saidlens and being adapted to temporarily halt the forward motion of saidbelt for exposure to an image projected by said lens, a dusting chamberhaving an opening adjacent the surface of said belt for dusting saidlayer and transfer means including a roller for rolling a transfer sheetagainst said layer to transfer dust from said layer to said transfersheet.

9. In combination, an electrophoto plate comprising a layer ofphotoconductive insulating material, and means for electrostaticallycharging said layer preparatory to photographic exposure thereofcomprising a rotary brush, means for rotating said brush, and means forsimultaneously moving said plate and brush relative to each other tobring all parts of said layer into frictional engagement with saidbrush.

10. In combination, means for moving a layer carrying an electrostaticcharge image in a path parallel to its surface, and means for dustingthe surface of said layer with electroscopic powders comprising aplurality of dust chambers having openings therein adjacent the path oftravel of said surface, means individual to each of said chambers foragitating dust in said chambers, and means for selectively operatingsaid agitating means.

11. An electrophotographic copying machine comprising in combination, anelectrophoto plate comprising a layer of photoconductive insulatingmaterial and means for moving said plate through a series of positionsin sequence in a path parallel dust from said layer to said to its ownsurface, a frictional charging member for electrostatically chargingsaid layer by friction in the first of said positions, light imageprojecting means for projecting a light image onto said layer in thesecond of said positions, a dusting device for dusting said layer in thethird of said positions, transfer means for pressing a dust receivingsheet against said layer in the fourth of said positions, and platecleaning means to clean off residual dust on said plate in the fth ofsaid positions.

12. An electrophotographic copying machine comprising, in combination,an electrophoto plate having a bare layer of photoconductive insulatingmaterial on its surface, a frictional charging brush, means for bringingsaid brush into frictional contact with said layer to charge said layer,and a conductor in contact with said brush to drain oi accumulatedcharges thereon.

13. An electrophotographic copying machine comprising, in combination.an electrophoto plate having a bare layer of photoconductive insulatingmaterial on its surface, means for charging said layer and means forsubsequently rolling a master sheet to be copied against said layer andilluminating said layer through said master sheet, said rolling meansincluding alight transmitting pressure applying layer.

14. An electrophotographic copying machine comprising, in combination,an electrophoto plate having a bare layer of photoconductive insulatinging said layer in sequence and means fox` transferrng the dust therefromto a transfer sheet, and a heating element adjacent to said electrophotoplate to disperse moisture from the surface of said layer.

16. A device for transferring a configuration of thermoadhesive dustparticles from a surface to a sheetcomprising, in combination, a bodyhaving a surface carrying a design of looselyadhering dust particles, aroller for rolling said sheet against said surface and a heater forpreheating said sheet prior to its contact with said surface, saidheater having a heated surface for pressing against the dust-engagingface of said sheet.

17. A device for transferring a configuration of dust particles from asurface to a sheet comprising, in combination, a body having a surfacecarrying a design of loosely adhering dust particles, a roller forrolling a sheet against said surface and means for wetting the dustreceiving side of said sheet prior to its contact with said surface.

18. A device for transferring a configuration of thermo-adhesive dustparticles from a surface to a sheet comprising, in combination, a bodyhaving a surface carrying a design of loosely adhering dust particles, aroller for rolling a sheet against said surface and means forpre-heating said sheet prior to its contact with said surface.

19. An electrophoto plate comprising a conductive layer, a layer ofphotoconductive insulating material adhering to the surface thereof anda design permanently adhering to the surface of said photoconductivelayer, said design being formed of insulating material.

20. An electrophoto plate comprising a conductive backing sheet, acoating of photoconductive insulating material on said sheet and e.design of insulating material on said photoconductive coating, wherebyan electrostatic latent image may be produced on said plate comprisingportions formed by the electrostatic charge on said insulating materialdesign and other portions formed by modication of the electrostaticcharge condition of said photoconductive coating resulting from exposureto an optical image.

CHESTER F. CARLSON.

